Keystroke-Level-Model

The Keystroke-Level Model (KLM) predicts how long it will take an expert user to accomplish a routine task without errors using an interactive computer system. It was proposed by Stuart K. Card, Thomas P. Moran and Allen Newell in 1980 in the Communications of the ACM and published in their book "The Psychology of Human-Computer Interaction" in 1983, which is considered as a classic in the HCI field. The foundations were laid in 1974, when Card and Moran joined the Palo Alto Research Center (PARC) and created a group named Applied Information-Processing Psychology Project (AIP) with Newell as a consultant aiming to create an applied psychology of human-computer interaction. The KLM is still relevant today, which is shown by the recent research about mobile phones and touchscreens (see Adaptions).

Step terminology

Kieras (1993, 2001) defines the following operations:

Code	Operation		Time
K	Key press and release (keyboard)	Best Typist (135 wpm)	0.08 seconds
		Good Typist (90 wpm)	0.12 seconds
		Poor Typist (40 wpm)	0.28 seconds
		Average Skilled Typist (55 wpm)	0.20 seconds
		Average Non-secretary Typist (40 wpm)	0.28 seconds
		Typing Random Letters	0.50 seconds
		Typing Complex Codes	0.75 seconds
		Worst Typist (unfamiliar with keyboard)	1.20 seconds
P	Point the mouse to an object on screen		1.10 seconds
B	Button press or release (mouse)		0.10 seconds
H	Hand from keyboard to mouse or vice versa		0.40 seconds
M	Mental preparation		1.20 seconds
T(n)	Type string of characters		n × K seconds
W(t)	User waiting for the system to respond
D(n0, l0)	Draw n0 straight line segment with mouse of total length l0 centimeters

A mouse click would be written "BB" (button press, button release) while a sequence of 3 keyboard key presses is "KKK" or "T(3)" ("T" stands for "type").

A common operation that involves pointing and clicking something on the screen would be written "MPBB" (think, point, press, release).

KLM is not the only technique for evaluating interfaces, but it can be used to compare the speed of two different interfaces designed to accomplish the same task.

Testing steps

The following 11 steps were developed based upon the methodologies and ideas of Kieras and Olson-Olson and describe the proper approach to calculate the time it takes to complete a task by using a computer interface and hardware.

Step 1 — Obtain a working prototype of computer interface or a step by step operational description of a task.

Step 2 — Identify the goals or the desired outcome of work .

Step 3 — For each of these goals, find subgoals or tasks that achieve the main goals.

Step 4 — Identify methods to main goals and all subgoals.

Step 5 — Convert description of methods to pseudo-code (the terminology that is described above).

Step 6 — State any and all assumptions used in the making of pseudo-code and goals.

Step 7 — Determine appropriate mental or keystroke operators for each step.

Step 8 — Assign time values to mental or keystroke operators.

Step 9 — Add up execution times for operators.

Step 10 — Adjust total time of task to be sensitive by age of expected users.

Age (years)	Time Adjustment Multiplier (Multiply task time by this value)
Use as is
30–40	???
40–55	By 1.4
55–60	By 1.7
> 65	By 2.2

Step 11-Validate results

Example Calculation

Change the code in Line 512 from "hte" to "the" ('the'the' in computer language) and then press Enter Key

or

" Change 512 'hte'the' "

Steps

• Mentally prepare
• 6 average speed keystrokes (for word "change")
• 1 average speed keystrokes for space bar
• 3 keystrokes for pressing numbers "512"
• 1 average speed keystrokes for space bar
• Mentally Prepare by reading what needs to be changed
• 6 average keystrokes for typing Vorlage:Not a typo and the
• 3 keystrokes to press the 3 " ' "
• 1 keystroke to press Return Key

Values

K1 = average speed keystrokes (0.20 seconds)

K2 = typing random letters (0.50 seconds)

M = Mentally Prepare (1.35 seconds)

Put above steps into formula: M + 6K1 + K1 + 3K2 + K2 + M + 3K1 + K2 + 3K1 + K2 = 2M + 14K1 + 6K2 = 9.82 seconds

This method assumes that operator times are invariant and do not depend on the previous sequence of events. New physical operators can be added if their timing can be represented as a simple context-free function. KLM-GOMS does not account for either slips or mistakes automatically—the analyst must create separate models of error sequences and perform their own sensitivity analysis.

The placement of the keystrokes and pointer operations are straightforward, but the placement of the mental operations is not. Mental operations are placed by a set of rules that require some interpretation, such as determining a conceptual "cognitive unit" or grouping of actions. For instance, pressing ctrl and c simultaneously to perform a "copy" would be considered a single cognitive unit. Mental operations are inserted before each cognitive unit to account for cognitive preparation and decision-making.

The main reason a designer or analysts would use this technique is that it is a very fast. Different designs or systems can be compared against one another quickly. It does not require that the evaluator be an expert in GOMS because the procedure is an explicitly laid out recipe. A major caution is that the algorithm is designed to estimate the execution time for an expert user, which is typically faster than the time for a new user or an unfamiliar task.

See also

• Human information processor model
• CMN-GOMS
• CPM-GOMS

External links

• Simple KLM calculator (free, downloadable Windows app)
• The KLM Form Analyzer (KLM-FA), a program which automatically evaluates web form filling tasks (free, downloadable Windows app).
• The CogTool project at Carnegie Mellon University has developed an open-source tool to support KLM-GOMS analysis.
• GOMS by Lorin Hochstein

References

Notations

• This article incorporates text from Dr. G. Abowd: GOMS Analysis Techniques – Final Essay, (link do not work) which has been released into GFDL by its author (see [1]).
• Vorlage:Citation
• Vorlage:Citation